The present invention relates to methods and compositions for treating subterranean formations. More particularly, the present invention relates to treatment fluids that comprise a methyl ester sulfonate (“MES”) surfactant, and associated diverting methods.
Viscosified treatment fluids may be used in a variety of subterranean treatments. Such treatments include, but are not limited to, drilling operations, stimulation treatments, and sand control treatments. As used herein, the term “treatment,” or “treating,” refers to any subterranean operation that uses a fluid in conjunction with a desired function and/or for a desired purpose. The term “treatment,” or “treating,” does not imply any particular action by the fluid.
The diversion of treatment fluids in subterranean operations is well known and may be desirable in a variety of subterranean operations, such as in acid stimulation operations, injection operations, scale inhibition operations, and clay stabilization operations. In many instances, diversion is desirable because the treatment fluid may preferentially enter portions of a subterranean formation with high permeability at the expense of portions of the subterranean formation with lesser permeability. For example, in acid stimulation operations, it may be desired to contact less permeable portions of the subterranean formation with the treatment fluid containing an acid so as to achieve the desired stimulation. In other instances, it might be desired to divert a treatment fluid away from certain portions (e.g., water-producing portions) of a subterranean formation entirely so as to treat other portions (e.g., hydrocarbon-producing portions) of the subterranean formation. In scale inhibition operations and clay stabilization operations, it may be desirable to divert the treatment fluid so as to obtain a uniform distribution of the treatment fluid throughout the subterranean formation regardless of the permeability of the particular portion thereof.
A variety of techniques have been used to divert treatment fluids to less permeable portions of a subterranean formation. Such techniques have involved, among other things, the injection of particulates, foams, or blocking polymers (e.g., crosslinked aqueous gels) into the subterranean formation so as to plug off the high-permeability portions of the subterranean formation, thereby diverting subsequently injected fluids to less permeable portions of the subterranean formation. In certain techniques, a treatment fluid is placed adjacent to a high-permeability portion of a subterranean formation, and the treatment fluid is viscosified so as to form a gel that, inter alia, temporarily plugs the perforations or natural fractures in that portion of the formation. When another treatment fluid encounters the gel, it is diverted to other portions of the formation. While these diversion techniques have been used successfully, each technique also has disadvantages. First, in some instances, plugging off the high-permeability sections may not be suitable for a producing formation, for example, because the injected solution (or material) may reduce or stop the flow of hydrocarbons in addition to the achieving a desired diversion of the treatment fluid. Expensive and/or time-consuming remedial treatments may be required to remove the injected solution (or material) and/or to return the formation to production. Furthermore, techniques geared toward injecting solutions (or materials) designed to plug off high-permeability portions of the subterranean formation may require expensive zonal isolation, which may be inaccurate or lead to inadvertent plugging of and/or damage to the hydrocarbon-bearing sections. Moreover, polymeric gelling agents may leave an undesirable residue in the subterranean formation after use. As a result, potentially costly remedial operations may be required to cleanup the fracture face and proppant pack.
To combat these problems, some surfactants have been used as gelling agents in diverting treatments. Certain surfactants, when mixed with an aqueous fluid having a certain ionic strength, are capable of forming a viscous fluid that has certain elastic properties, one of which may be shear thinning. Surfactant molecules (or ions) at specific conditions may form micelles (e.g., worm-shaped micelles, rod-shaped micelles, etc.) in an aqueous fluid. Depending on, among other things, the surfactant concentration, and the ionic strength of the fluid, etc., these micelles may impart increased viscosity to the aqueous fluid, such that the fluid exhibits viscoelastic behavior due, at least in part, to the association of the surfactant molecules contained therein. The viscoelastic fluid then may plug off a high-permeability section of the subterranean formation and divert treatment fluids subsequently introduced into the subterranean formation to less permeable sections of the formation. Further, because the micelles may be sensitive to the pH and hydrocarbons, the viscosity of the viscoelastic fluid may be reduced after introduction into the subterranean formation without the need for conventional gel breakers (e.g., oxidizers). This may allow a substantial portion of that fluid to be produced back from the formation without the need for expensive remedial treatments. However, surfactants used heretofore as gelling agents tend to have undesirable environmental characteristics (e.g., toxicity) and/or may be limited by strict environmental regulations in certain areas of the world.